Clock pins when running on internal clock

No different than any other pin. Leaving it floating is generally not advised (especially if you care about consumption).

It's best to ground the unused pins through a 10K pull-down resistor and set them as analog inputs to disable the Schmitt triggers on the pins (which are required when the pin is in the default digital input state).

AN3430 ( https://www.st.com/content/ccc/resource/technical/document/application_note/77/74/4f/da/9b/9c/43/e7/DM00033348.pdf/files/DM00033348.pdf/jcr:content/translations/en.DM00033348.pdf ) recommends this:

• At the startup of the application:

1. Enable all GPIO clocks
2. Configure all I/Os in analog input mode
3. Disable all GPIO clocks

• In the main application:

1. Enable the required GPIO clock
2. Configure the required I/Os on the application

• I/O configuration trick:

1. If the user application just needs the I/Os to configure it as a peripheral alternate function in order to output or input signals (no read or write from/to GPIO registers), we recommend disabling the associated GPIO clock of the used I/Os after configuration. In this case I/O signals are still available and we optimize the GPIO current consumption by disabling its clock.

• I/O toggling frequency:

1. When configuring the I/O, pay specific attention to the I/O speed value configured in OSPEEDR (2 MHz, 10 MHz, 25 MHz, 50 MHz and 100 MHz). Current consumption is as high as the I/O toggling frequency, so, to optimize current consumption, OSPEEDR should be configured with the lowest possible value.

​Thanks !

I forgot to mention in my question that i meant "floating" in hardware aspect

Regarding the analog input - of course !

Thanks anyway ! :)